This invention relates to a ground-engaging tool, and more specifically to a ground-engaging tooth for an excavation bucket.
Conventional ground-engaging teeth for excavation buckets generally are designed to be replaced when worn. In some of the known arrangements, the teeth comprise one-piece tips which are welded to a lip on the bucket and which have to be cut off the lip when replaced. In other arrangements, each tooth includes an adaptor which is either releasably attachable to a nosepiece on a bucket lip or is welded directly to the bucket lip, and a tip which is releasably attachable to the adaptor, typically with a locking pin. This type of tooth is replaced by removing the locking pin and sliding the tip off the adaptor.
In certain applications, for example dragline operations, the tips are exposed to excessive abrasion and tend to wear down relatively quickly so that it is necessary to replace these tips fairly often. Since replacement of the ground-engaging teeth interrupts the dragline operation, it is desirable to have relatively durable teeth which do not require frequent replacement.
For the purpose of this specification, the term xe2x80x9cexcavatexe2x80x9d includes the operation of a dragline, and accordingly reference to an xe2x80x9cexcavation bucketxe2x80x9d should be understood to include a dragline bucket.
According to the invention there is provided a ground-engaging tool which is connected or connectable to a lip on an excavation bucket, the ground-engaging tool comprising:
a tool body which is formed from a material having a hardness greater than or equal to 35 Rockwell C hardness and which defines a contact surface at one end for receiving impacts; and
a hardened core extending through at least a substantial portion of the tool body from the contact surface or a region approximate the contact surface for transferring impacts through the tool body, the hardened core being formed from a material having a hardness which is at least 20% greater than the hardness of the material of the tool body.
Typically, the contact surface is sized so as to present a blunt edge at one end of the tool body.
In a preferred embodiment of the invention, the hardened core is in the form, of a cylinder and the longitudinal axis of the core is offset relative to the longitudinal axis of the tool body.
In a particularly preferred embodiment, the tool body is formed from a steel which has a yield strength of approximately 700 MPa and which is heat treated to a hardness of approximately 40 Rockwell C hardness, and the hardened core is formed from a Tungsten Carbide having a hardness of approximately 83.5 Rockwell A hardness.
The tool body may be machined and the core may be press fitted into a pre-formed hole in the tool body. In this case, an adhesive may be applied to the core prior to insertion into the tool body.
Alternatively, the ground-engaging tool may be formed in a casting process.
In one arrangement, the tool body is designed to be welded to the lip of the excavation bucket.
In another arrangement, the tool body includes a formation which is releasably connectable to an adaptor on the lip of the excavation bucket.
Typically, the tool body tapers inwardly towards the contact surface.